# Chem 1B Thermodynamics

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27 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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Chem 1B

Thermodynamics

1.

A scuba tank is left out in the sun. Predict the following

for the gas in the tank
.

a.

q
>

0

q

<

0

q = 0

b.

w
>

0

w
<

0

w = 0

c. ∆ E
>

0 ∆E
<

0 ∆E = 0

2.

Spraying an aerosol

occurs so rapid
ly, there is no time for heat to be transferred
. Predict
the following

for the aerosol’s gas.

a.

q
>

0

q
<

0

q = 0

b.

w
>

0

w
<

0

w = 0

c. ∆ E
>

0 ∆E

<

0 ∆E = 0

3. Neon gas is compressed into a glass tube
isothermally. Predict the following.

a.

q
>

0 q

<

0 q = 0

b. w
>

0 w
<

0 w = 0

c. ∆ E
>

0 ∆E
<

0 ∆E = 0

4.

What is the

larger value
for argon
C
v

or C
p
? Explain.

5.

Which substance

has the larger value
of
C
v

,
hydr
ogen or helium? Explain.

6.

What is the change in internal energy when 3 mol of Ne is
cool
ed in a rigid container
from
400

°C to
25

°C?

7.

A hot air balloon requires 4.8 x 10
9

J of heat to inflate it from 2.3 x 10
7

L to 5.7 x 10
7

L at
sea level. Calculate q,

w, ∆H and ∆E for this process.

8.

For the following reactions at constant pressure, predict if ∆H
>

∆E, ∆H
<

∆E, or ∆H =
∆E. Calculate the difference for the inequalities

at 300K
.

a. H
2

(g)

+ Cl
2

(g)

2 HCl
(g)

b.
N
2

(g)

+ 3

F
2

(g)

2 NF
3

(g)

9.

Calculate
q and ∆E when 4.3 mol of liquid is vaporized at it
s

boiling point (73°C) and 1
atm pressure. ∆H
vap

= 28.6 kJ/mol at 73°C.

10.

Calculate the amount of heat that is released when
12 g of ammonia reacts with 25

g of
oxyg
en according to the following reaction.

4 NH
3

+ 5 O
2

4 NO + 6 H
2
O ∆H =
-
338 kJ

11.

A 25.0 g piece of unknown metal was transferred

from an oven at 115 °C
into a coffee cup
calorimeter containing 150. mL of water at 24 °C and allow
ed to come to equilibrium
where the t
emperature was measured to be 28

°C. Calculate the specific heat capacity of
the metal. (C
cal

= 25 J/K and C
water

= 4.18 J/g°C)

12.

In a coffee cup calorimeter 50.0 mL of 0.10 M NaOH and 20.0 mL of 0.30 M HCl are
mixed.

The temperatures before and after the reaction were measured to be 23.0°C and
31
.0
°C. Calculate the molar enthalpy change for the neutralization reaction. Assume no
heat is absorbed by the calorimeter. The density of each solution is 1.0 g/mL and the
s
pecific heat capacity for each solution is 4.18 J/g°C.

13.

Instant ice packs have a packet of NH
4
NO
3

which upon cracking is released and
dissolved in water. If 15 g of NH
4
NO
3

is dissolved in 250 mL of water the solution cools
22°C. Calculate the molar enth
alpy change for the dissolution of NH
4
NO
3
. Assume no
heat is lost to the surroundings. The specific heat capacity for the solution is 4.18 J/g°C.

14.

Calculate the final temperature when 38 mL of 0.15 M Pb(NO
3
)
2

is mixed with 42 mL of
0.23 M KI both initial
ly at 23 °C. Assume no heat is lost to the surroundings. The
specific heat capacity for the solution is 4.18 J/g°C

and the density is 1.0 g/mL.

Pb
2+

+ 2 I
-

PbI
2

∆H =
-
2
97 kJ/mol

15.

How many grams of methane would you have to burn t
o heat up 250 mL of water by
78°C? The heat of combustion for methane is
-
803 kJ/mol. The specific heat capacity of
water is 4.18 J/g°C.

16.

Given the following data calculate the ∆H° for the reaction
:

NO

+

O

NO
2

2 O
3

3 O
2

∆H° =
-
427 kJ

O
2

2 O

∆H° = +495 kJ

NO + O
3

NO
2

+ O
2

∆H° =
-
195 kJ

17.

The standard heat of formation for
gaseous
PF
5

is
-
1578 kJ/mol. Write out the
corresponding reaction.

18.

Calculate ∆H° for the following:

a.

condensation of
0.82 mol
water

b.

combustion of

55 g
liquid ethanol
(C
2
H
6
O)

19.

When 17 g of liquid benzene (C
6
H
6
) is burned 91 kJ of heat is released,
calculate the
standard heat of formati
on for
benzene.

20.

Determine if ∆
S is positive or negative
for the following
under standard conditions
.

a.

melting ice

b.

formation of gaseous NF
3

c.

precipitation of AgCl

21.

Which has the greatest entropy?

a.

1 mol of He at STP or 1 mol of He at standard conditions

b.

1 m
ol of Ar at STP or 2 mol of Ar at STP

c.

1 mol of Ne at STP or 1 mol of CH
4

at STP

d.

1 mol of Cl
2

at STP or 1 mol of F
2

at STP

22.

The molar entropy of helium gas at 25 °C and 1.00 atm is 126.1 J/molK. Assuming ideal
behavior, calculate the entropy for 0.100 mol

of He (g) at 25 °C and a volume of 5.00 L.

23.

Calculate
∆S and w when 46 g of water is heated from
-
22°C to 156 °C

at a constant
pressure of 1 atm. The heat capacities for solid, liquid and gaseous water are 2.03 J/g°C,
4.18 J/g°C and 2.02 J/g°C respective
ly. The enthalpies of fusion and vaporization are 6.01
kJ/mol and 40.7 kJ/mol respectively.

Substance

∆H° (kJ/mol)
=
e
2
O
( l )

-
286

H
2
O
( g )

-
2
42

C
2
H
6
O
( l )

-
278

CO
2

( g)

-
393.5

24.

4.0 mol of He at 298 K is allowed to expand reversibly and isothermally to twice its
original volume
. Calculate q, w and ∆E for this process.

25.

For the freezing o
f water at
-
10 °C and 1 atm, predict whether ∆H, ∆S, and ∆G should be
positive negative or zero.

26.

At what temperatures would the dissociation of hydrogen be spontaneous?

H
2

(g)

2 H
(g)

27.

For ammonia the enthalpy of fusion is 5.65 kJ/mol and the
entropy of fusion is 28.9
J/molK. Will solid ammonia spontaneously melt at 200. K? What is the approximate
melting point of ammonia?

28.

Use the following reaction to answer the following.
2 SO
2

(g)

+ O
2

(g)

2 SO
3

(g)

a.

Calculate ∆G°

b.

Calcul
ate ∆G at 1000 °C if the pressures for SO
2
, O
2

and SO
3

are 40 atm, 15 atm
and 0.12 atm respectively.

c.

What is the equilibrium constant at this temperature?

Substance

∆G
f
° (kJ/mol)

SO
2

(g)

-
300

SO
3

(g)

-
371

29.

For a certain reaction the K
p

is 50 at 25 °C
and 9 x 10
8

at 110 °C.

a.

Is the reaction endothermic or exothermic?

b.

Calculate ∆H
°

c.

What is K
p

at
75 °C?